Top Australian Trees: #2 Tropical Queensland

(Editor's Note:This article was originally publishsed on May 8, 2008. Your comments are welcome, but please be aware that authors of previously published articles may not be able to respond to your questions.)

In this article we head north to the warm state of Queensland, where beautiful plant-life abounds. Choosing only five species has remained a difficult task, resulting in the exclusion of many beautiful species. Once again, the thumbnail - featuring blossoms of the Pink Flame Kurrajong, Brachychiton discolor - comes courtesy of the Australian Plants Society.

Bunya Pine (Araucaria bidwillii)

Commencing our tour in south-eastern Queensland, we meet the Bunya Pine or False Monkey Puzzle in one of its few remnant habitats. This is an ancient conifer from the same family as the Norfolk Island, Hoop, Kauri & Wollemi Pines. Millions of years ago, this tree was widespread across the east side of the Australian continent & had relatives in the Northern Hemisphere. Over the aeons since, Araucarias north of the equator have all disappeared & the Bunya, reduced to a handful of isolated stands scattered along the Queensland coast.

Evolved to survive in a world of dinosaurs, the Bunya is a large tree. It is not a true pine but does form monstrous pine-like cones, which are known for two main reasons. One is the edible nuts that can be found in them. The other is a common antecdote; that they can be lethal in late summer & early autumn, when they fall from great heights. Mortal threats aside, Bunya nuts are tasty with a flavour similar to pine nuts. They are popular amongst both locals & also, several species of macropod (large footed marsupial) believed to be the tree's main seed spreaders [1]. In the ancients past, scientists believe this same task may have been performed by dinosaurs.

The large fruit dropped by Bunyas are female cones. These can grow to around 1 & ½ times the size of a regular pineapple. The male cones are much smaller. The tree prefers a warm climate, but can grow quite large in temperate areas. There are a number of specimens in Sydney for example, that stand well over 40 metres. Judging by these trees, the species will survive high winds, light frosts & some irregularity in rainfall.

Like all Araucarias, Bunyas are attractive, resilient trees that offer the chance to cultivate conifers over a broader range of climes. Ultimately of course, size will be an important consideration as these trees live hundreds of years & can reach up to 50 metres. In Australia, Bunyas are not quite as popular as some other Araucarias like the Norfolk Island Pine, but they are sometimes grown for their nuts. There are a number of local recipes that feature Bunya nuts, including a fruit or Christmas cake featured on the ASGAP page below.

The Bunya's female cone is huge, as are the nuts inside. Oddly, my dog likes to eat them

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Illawarra Flame Tree (Brachychiton acerifolius)

The warm rainforests of eastern Australia start in coastal New South Wales & wander north across the Queensland border, toward the Tropic of Capricorn. Skirting the edges of this steamy regime can be found Brachychiton acerifolius, the Couramyn, Illawarra Flame Tree or Flame Kurrajong. B. acerifolius is probably the most well known member of the Kurrajong or Bottletree family; an interesting genus that houses 30 magnificent Australian trees & shrubs. Broadly speaking, Brachychitons are a drought-adapted group. They share characteristics such as a tendency to shed leaves during drought & over the dry northern winter. At the end of this dry season is when Kurrajongs flower, which they do in magnificent style [2].

Brachychiton acerifolius

The Flame Tree is medium-sized, reaching around thirty metres in the wild & usually much less when cultivated. It gains its botanical name from its attractive, maple-like leaves. These are large, dark & clearly lobed. The tree's common name is derived from its spectacular flowering habits. The bright scarlet flowers are profuse & bell-shaped, appearing in clusters at the ends of the branches. These are followed by large seed pods filled with powdery, yellow seeds.

The deciduous nature of the Flame Tree depends upon rainfall. During wet years, it may retain some of its leaves or even remain evergreen when grown in temperate regions. Like its pachycaul relatives, B. acerifolius is sensitive to heavy frost & has adpated to dry winters. It should be sheltered from excessive rain & watered sparingly over the colder seasons.

Come spring Flame Kurrajong's can earn their name, rewarding gardeners with a display that lead many to consider it possibly Australia's most beautiful native tree. Flowering can be irregular & take five or more years from germination but this Kurrajong will be happy in a wide range of soils & climates. As with many Australian trees, the beauty & hardiness of the Flame Tree make it suitable for containers & bonsai training. It can be kept indoors in bright, sun-lit postions.

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Queensland Bottle Tree (Brachychiton rupestris)

Amongst the 31 Brachychiton species, there are a number of pachycauls or bottle trees. Perhaps the most distinctive of these is Brachychiton rupestris, the Queensland-Flaschenbaum, Narrow-leaf Bottle Tree, Queensland Bottle Tree or Bottle Kurrajong.

Like other bottle trees such as B. discolor, B. australis & B. populneus, this is a fat, water-storing species. Even in the wild, it will not grow beyond 20 metres high. With age though, its trunk can reach two metres in diameter as it swells into the tree's characteristic bottle shape. Like other Kurrajongs, B. rupetsris prefers a dry winter over which it will drop its leaves before flowering in the spring. The Queensland Bottle Tree's flowers are yellow & form in bell-shaped clusters, though less conspicuously than the Flame Tree.

Bottle Trees are easily propogated & will grow in a wide range of climates & soils. Being caudiciforms, they are resilient & stand transplantation more than most trees. For this reason plus the tree's showy trunk & strikingly thin leaves, B. rupestris makes another excellent bonsai or container specimen. It would suit many collectors & also serves as a great feature tree in parks & gardens. Since even mature trees will survive uprooting & months of transportation, many botanic gardens around the world feature B. rupestris [1].

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Macadamia Tree (Macadamia sp.)

The genus Macadamia belongs to Proteaceae or the Protea family which includes Grevillea, Hakea & Banksia amongst other Australian native groupings. There are many species of macadamia now identified, but only two produce edible nuts. These are the smooth-shelled M. integrifolia & the rough-shelled M. tetraphylla. The former is the preferred nut for roasting & has the greater commercial significance.

Aborigines are believed to have eaten both the rough & smooth-shelled nuts, but they were not discovered by Europeans until the 1850s. Since that time, the popularity of macadamias has grown worldwide with the establishment of plantation industries, first locally & then in Hawaii [3].

"Macadamias are considered the world's finest nut and are the only native Australian plant to become an international food. Their delicate flavour, versatility and crunchy texture make them a delight to consume. Also they contain a range of nutritious and health promoting constituents and form an important part of a healthy diet. A balanced diet containing macadamias promotes good health, longevity and a reduction in degenerative diseases."

Proteaceae is a "good example of a Gondwanan family, with taxa occurring on virtually every land mass considered a remnant of the ancient supercontinent Gondwana. The family and sub-families are thought to have diversified well before the fragmentation of Gondwana, implying that all of them are well over 90 million years old."

M. integrifolia nuts were once known as Queensland or Bauple nuts. The latter name descends from Mount Bauple, a region to which the species is naturally endemic. Mount Bauple is now home to a national park that is closed to the public & accessible only for scientific research. One of the reasons for this is the fact that M. integrifolia hybridises readily with M. tetraphylla & as a consequence, has become threatened in the wild [1].

So many appealing nuts like almonds, hazelnuts, & chestnuts needing chilly conditions, can be a frustration to gardeners in warm climates. Macadamia trees are a chance to get even. The natural choice is M. integrifolia, which grows to around 15 metres & spreads about the same. Relatively fast-growing, it will produce far ahead of most cool climate nut trees. In spring, these macadamias put on an attractive show of blossom chains known as racemes. These soon become clusters of young nuts that mature for roasting by late summer.

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Firewheel Tree (Stenocarpus sinuatus)

Another Proteaceaen family is Stenocarpus. This genus boasts around 25 species of shrubs & trees, mostly from New Caledonia. Some of these are threatened by habit loss, with at least one species - S. dumbeensis - recently becoming extinct [3].

Of the nine Australian species, S. sinuatus, the Queensland Firewheel Tree is probably the most dazzling. In some ways this tree is similar to the Flame Kurrajong & in others, it is much like its Macadamia cousins. The Firewheel gains its common name from its striking flowers. These sprout flaming red from circular bracts, covering the tree through summer much like a fireworks display. The leaves are deeply lobed but otherwise typically Proteaceaen. That is, tough, waxy & serrated like those of Macadamias, Proteas & Banksias. The juvenile leaves have an attractive ted tint.

Firewheel Trees grow to around 30 metres in the wild, though they can be cultivated in subtropical & temperate areas for a more diminuitive result. In Australia, they can be seen growing as far south as Melbourne. Being a rainforest species, this tree requires regular watering, prefers loamy, well drained soils & will be happy in full sun or partial shade.

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Stenocarpus sinuatus

Stenocarpus salignus, the Scrub Beefwood or Cruet of Eggcups is essentially a white flowering alternative to the Firewheel Tree. Both species occur naturally along the north-eastern coast of the continent & have the same cultivating requirements.

S. sinuatus is popular in both private gardens & public areas such as parks & nature strips. It can be propagated readily from fresh seed & somewhat less reliably, from cuttings. It is an excellent tree for container-growing, both indoors or outdoors & whilst flowering, attracts nectar-feeding birds.

Footnotes:

A life-long vegetarian, community gardener & member of Australia's SeedSavers network. I love plants both within the garden & in the wild. Trees are a special passion that I hope will prove infectious.